Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications, including ambient lighting, signage, advertising, display lighting, and backlit lighting. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects.
Due in part to advances in LED technology, illumination systems directed toward lighting applications such as those listed above are progressively becoming more sophisticated. For example, an illumination system can be provided which can control the color and intensity of multiple LEDs in a lighting system in response to real-time inputs. Furthermore, multiple illumination systems may coordinate to provide expanded functionality. As the level of sophistication of illumination systems increases, it becomes feasible and beneficial to integrate illumination and communication features into a single system. Such integrated communication can be useful, for example for feedback purposes within an illumination system, or for coordination of multiple illumination systems.
One approach to the integration of illumination and communication functionality in a single system is to use at least one LED as a source of both illumination and information. This approach reduces cost and complexity of the system by using the radiant flux emitted by an LED to transmit information instead of a second signal source, such as an antenna or other communication device. For example, some conventional techniques contemplate direct modulation of a fluorescent light source for communication purposes by modulating the light source drive current to transmit information through an optical medium.
However, direct modulation of LEDs, such as is obtained by modulation of a drive current, can be inferior for some LED-based lighting systems. For example, although the radiant output of high-flux LEDs can be directly modulated at rates of up to several tens of megahertz by varying their electric drive currents, this approach may involve significant power losses during the modulation process if a time-varying signal is superimposed on an otherwise constant drive current. This direct modulation of LEDs can also be inefficient if the LED die is coated with phosphors that may have phosphorescence decay times of several milliseconds. In this situation, the radiant flux generated by the phosphors may need to be filtered in order to isolate the radiant flux (typically blue light) emitted by the pump LEDs, since it may be difficult to demodulate light emitted by the phosphors in this case.
Several conventional methods exist, however, for indirect control of light, which can be used for example to indirectly influence the radiant flux of light sources. For example a controllable lens or optical filter can be optically coupled to a light source, and the characteristics of said lens or filter can be varied, resulting in corresponding variation of light. Modulation of light in an illumination system through such indirect means could be advantageous due to increased energy efficiency.
For example, one method discloses a liquid lens with an electrically-controlled focus, comprising a light-transmitting liquid forming a lens interposed between two electrodes, the curvature of the surface of the liquid lens being controllable by varying the voltage between the two electrodes. Another conventional method uses a liquid lens as a light valve to modulate a dedicated light beam to record a sound track on photographic film. The method contemplates configuring the liquid lens surface as a single concave meniscus with variable concavity controllable by an applied voltage, and passing light through the lens onto photographic film. The variation of the lens concavity can cause corresponding variation in exposure intensity or exposure area on the photographic film, thereby recording information on the film. However, since only a single concavity is adjusted, a limited range of configurations can be used. In addition, precisely varying the concavity in time requires complex control circuitry. Yet another method discloses driving a liquid lens to produce standing or running waves on the surface thereof.
Thus, there is a need in the art to transmit information in an illumination system, using the liquid lens.